#include <iostream>

using namespace std;

int fib(int n) {
	if( n == 1 )
		return 0;
	if( n== 2 ) {
		return 1;
	}
	return fib(n-1) + fib(n-2);
}

int main()
{
	int n;
	cin >> n;
	cout << fib(n) << endl;
	return 0;
}
